[sane-devel] Scanning produces black images

[Gerhard Jaeger]

On Sonntag, 15. April 2007, JKD wrote:
> El Sun, 15 de Apr de 2007, a las 09:58:08PM +0200, Magnus Rosenbaum dijo:
> > I upgraded my Linux kernel from 2.6.18 to 2.6.19 and noticed a strange
> > behaviour in xsane and also in kooka: The program acts als it would
> > normally scan, but the scanner does not do anything and the result is a
> > completely black image.
> > 
> > However scanning with scanimage works allright!
> > 
> > The behaviour is reproducible with kernel 2.6.19 and also 2.6.21-rc5. When
> > I boot 2.6.18 scanning works as expected again.
> > 
> > Does anyone have an idea, how I could further investigate this problem?
> 
> Some days ago a user reported the same issue. For some unknown reason,
> with newer kernels some backends are experiencing problems, retrieving a
> black image from scanner. This is my experience about this issue with
> hp3900 backend:
[SNIPSNAP]
>
> I don't really know what the real problem is. Perhaps backends must be
> compiled against current library or kernel versions. Once compiled,
> problem is fixed.

This is also an issue with the Plustek backend, reported by various
Ubuntu and Gentoo users. As already stated by PhobosK, the problem is
the kernel option CONFIG_USB_SUSPEND. This in deed is needed for laptop
users. It is currently marked as "experimental" but already used by various
distros. 

I think the problem really is, that libusb does not know anything about that
suspend stuff and therefore we have more or less no possibility to wakeup
the port, where the scanner is connected to.
One thing that could be observed: In all cases, scanimage works fine - guess
this is because it never closes the port until the scan process is done.

Any ideas around?

Gerhard